A laser robot such as a polar coordinates laser robot is disclosed in International Application No. PCT/JP90/01627. The disclosed laser robot receives a laser beam emitted by a laser oscillator, i.e., a laser light source provided outside the robot unit and transmitted to the robot unit. The laser beam is further transmitted by laser beam reflecting mirror units disposed respectively at the joints of the robot unit to travel along an optical path aligned with the axes of rotation of the joints to an extremity of the robot unit, and irradiates an irradiation object while being focused by a focusing device provided on the extremity of the robot unit and including a parabolic focusing reflector and an irradiating nozzle.
The position and angle of incidence of the laser beam on the laser beam reflecting mirror unit disposed at each joint must be accurately adjusted so that the laser beam is accurately transmitted to the focusing device provided on the extremity of the robot unit. When the laser beam is transmitted from a laser beam receiving position on the robot unit along an ideal optical path to the focusing device, the laser beam can be focused on a spot having a maximum energy density at an objective point on an object of irradiation, to enable the most effective cutting, welding or photochemical reaction.
Accordingly, the position and orientation of the laser beam reflecting mirror units disposed respectively in the joints of the robot unit of a laser robot are adjusted to adjust the optical path followed by the laser beam.
Referring to FIG. 8, when adjusting the optical path of a laser beam in a prior art laser robot by a prior art optical path adjusting method, an adjusting laser beam 8 emitted by a laser oscillator 7 is introduced through laser beam reflecting mirror units 9, 10 and 11 provided in a laser beam conduit line extended outside the robot unit of the laser robot into the robot unit. The adjusting laser beam is then reflected by laser beam reflecting mirror units 12, 13 and 14 provided respectively in the joints of a rotary robot body and robot arms, to thereby fall on a parabolic reflecting mirror 15 accommodated in a focusing device arranged on a robot wrist. The optical path followed by the adjusting laser beam reflected by the parabolic reflecting mirror 15 is detected by an optical sensor 16 disposed after the parabolic reflecting mirror 15 with respect to the direction of travel of the adjusting laser beam. For example, if the laser beam reflecting mirror unit 11 is shifted from a correct position indicated by continuous lines to a position indicated by dotted lines, the adjusting laser beam travels along an optical path, indicated by broken lines, not aligned with a correct optical path and falls on the parabolic reflecting mirror 15. Accordingly, if the adjusting laser beam moves in the optical sensor 16 when any one of the joints of the robot unit is turned, it is judged that the optical path followed by the adjusting laser beam is not aligned with the correct optical path and the position and orientation of the laser beam reflecting mirror units 12, 13, 14 and 15 provided in the joints are adjusted to adjust the position and angle of incidence of the adjusting laser beam on the laser beam reflecting mirror units 12, 13, 14 and 15 so that the adjusting laser beam does not move in the optical sensor 16 even if any one of the joints is turned.
The optical sensor 16 comprises a known semiconductor position detecting device, such as a position sensitive detector, and the adjusting laser beam is a beam of visible laser light, such as laser light emitted by a Helium-Neon laser. Therefore, the adjusting laser beam is focused in a visible luminous spot P on the matrix coordinate plane 16a of the optical detector 16 as shown in FIG. 9. Accordingly, it is possible to decide whether or not the optical path followed by the adjusting laser beam is in alignment with the axis of rotation of the joint from the observation of the luminous spot P of the adjusting laser beam on the matrix coordinate plane 16a; that is, if the optical path followed by the adjusting laser beam is in alignment with the axes of rotation of all the joints of the robot unit, the position of the luminous spot P remains unchanged even if any one of the joints is turned. Thus, if the position of the luminous spot P on the matrix coordinate plane 16a remains unchanged when any one of the joints is turned, it is determined that a correct adjustment of the optical path followed by the laser beam has been achieved, and thus the optical path followed by the laser beam in alignment with the axes of rotation of all the joints and the laser beam can be properly projected onto the object to be irradiated.
On the other hand, when the optical path followed by the adjusting laser beam is not correctly adjusted and the luminous spot P moves along a circular path on the matrix coordinate plane 16a, the laser beam reflecting mirror units are adjusted, to thereby adjust the optical path.
Nevertheless, when measuring and adjusting the optical path followed by the laser beam according to the prior art optical path adjusting method, that the luminous spot P of the adjusting laser beam on the matrix coordinate plane 16a of the optical sensor 16 may remain fixed at one point on the matrix coordinate plane 16a as shown in FIG. 9, and the measurement shows the optical path followed by the laser beam in alignment with the axis of rotation of the joint when only the same joint is turned, because the prior art optical path adjusting method is a single-point laser beam detecting system that detects the adjusting laser beam by the optical sensor 16 disposed at a point on which the adjusting laser beam is focused by the parabolic reflector 15.
For example, the laser beam reflected by the parabolic reflecting mirror 15 of the focusing device may fall on the optical sensor 16 along an optical path inclined at an angle .theta. to a true optical path, as shown in FIG. 9. Accordingly, if the laser robot is an articulated laser robot and the laser beam reflected by the parabolic reflecting mirror 15 falls on the optical sensor 16 along the optical path inclined at the angle .theta. to the true optical path, the luminous spot P on the matrix coordinate plane 16a may show the measured optical path following the laser beam to be correct.
Thus, the prior art method of adjusting an optical path followed by a laser beam is unable to accurately adjust the optical path followed by the laser beam when the optical path adjusting method is applied to an articulated laser robot.